Field of the Invention
The present invention relates to compounds which have a superior immunostimulatory effect and are useful as an immunostimulating agent, particularly an adjuvant. The present invention also relates to compositions containing such a compound, and vaccines containing such a compound and an antigen.
Discussion of the Background
Vaccines includes live vaccines wherein a pathogen is attenuated, whole particle vaccines wherein a pathogen is inactivated, and split vaccines wherein a pathogen is decomposed and only a particular component is extracted and purified. Of these, split vaccines require the addition of a compound or composition called adjuvant to enhance immunostimulatory ability thereof. Also, it is said that mucosal vaccines, cancer vaccines, and vaccines for a certain kind of allergy that are being increasingly researched and developed in recent years also require the addition of an adjuvant for the expression of the effects thereof. Examples of the adjuvants approved inside Japan at present include aluminum salts (aluminum hydroxide gel etc.) as precipitated adjuvant, squalane as oil adjuvant, MPL that is a variant of lipopolysaccharide LPS which is a constituent component of gram negative bacteria cell wall outer membrane intrinsically having immunogenicity. The research and development of adjuvants at the global level are also advancing taking note of nucleic acid derived from CpG and Poly I:C and the like, variants of bacteria constituent components that activate Toll-like receptor (TLR), variants of cytokines that stimulate immune system and the like. However, these existing adjuvants including those already approved inside Japan and those under research and development have the following problems.
As for aluminum salt which is a precipitated adjuvant, the adjuvant effect is questioned in some vaccines such as influenza HA vaccine, foot-and-mouth disease vaccine and the like. Also from the safety aspect, aluminum salt is known to often show granulation in the inoculation site, cause hyperimmunoglobulinemia E and the like. As for oil adjuvants such as squalene and the like, inoculation may be sometimes painful since viscosity increases by emulsifying, and inoculation site sometimes indurates since it has property to resist dispersion in the body and stay at the inoculation site. On the other hand, since MPL is a variant of LPS having immunogenicity, simultaneous inoculation with vaccine sometimes initiates strong inflammatory reaction, and sometimes accompanies pain and fever. Furthermore, adjuvants under development are also held to have safety problems such as allergy induction, strong inflammation reaction, fever initiation and the like. As for nucleic acid adjuvant, new problems are surfacing such as problems in synthesizing as a pharmaceutical product, for example, difficulty in chemical synthesis up to a chain length considered to afford an effective adjuvant effect and the like. Although adjuvants are requested to simultaneously show effectiveness and safety, conventional adjuvants already approved inside Japan and those under research and development fail to completely satisfy such request as the situation stands.
In the meantime, National Institute of Allergy and Infectious Diseases (NIAID) indicates the following 12 points regarding the safety of vaccine adjuvant. 1) free of induction of autoimmune response, 2) free of antigen having crossreactivity with human antigen, 3) free of induction of allergic hypersensitive reaction, 4) should be synthesized chemically pure, 5) free of carcinogenicity, 6) free of induction of response other than the object immune response, 7) should be a substance to be quickly metabolized in the body, 8) should be safe irrespective of inoculation method, 9) should be free of teratogenicity and reproductive toxicity, 10) should have preservation stability for at least one year, 11) should be selected for the object, 12) should tolerate side reaction developed at low frequency. Also, in the guideline of EMEA (European Medicine Agency) which is an organization responsible for examination of vaccine in Europe, 1) histological damage and granuloma formation of inoculation spot, 2) hypersensitivity and anaphylaxis, 3) pyrogenicity, 4) systemic toxicity, 5) reproduction toxicity, 6) genotoxicity (synthetic adjuvant alone) are recited as non-clinical toxicity test of adjuvant alone. While some parts are common or not common between US and Europe, at least the vaccine adjuvants to be developed from now should satisfy these requests.
As a compound having an immunomodulatory effect, for example, the compounds described in JP-A-4-230359; JP-A-59-219262; JP-A-63-264444; JP-A-62-63600; JP-A-5-507705; JP-A-11-302250; JP-A-5-186419; Cybulla, J. et al., Biochemical and Biophysical Research Communications 1980, 92(4), 1389-96; Zeelen, F. J. et al., Recueil des Travaux Chemiques des Pays-Bas et de la Belgique 1958, 77(3), 267-72; Roth, A. et al., Bioconjugate Chem., 2004, 15, 541-553; and Y. Aachoui et al., Cellular Immunology 271 (2011) 308-318, all of which are incorporated herein by reference in their entireties, have heretofore been reported. While Example 25 of JP-A-4-230359 discloses a compound wherein the group corresponding to R3 and R4 in the following formula (I) is an undecyl group (C11 alkyl group), the compound is different from a compound represented by the formula (I) and its adjuvant activity is not sufficient. While Example 3 of JP-A-59-219262 discloses a compound wherein the group corresponding to R3 and R4 in the formula (I) is an unsaturated hydrocarbon group (C17 alkenyl group), the compound is also different from a compound represented by the formula (I) and its adjuvant activity is not sufficient. While Tables 1 and 2 of JP-A-63-264444 disclose a compound wherein the group corresponding to R3 and R4 in the formula (I) is a long chain alkyl group (C35 alkyl group) substituted by a keto group or a hydroxyl group, the compound is also different from a compound represented by the formula (I), and dispersibility of the compound in saline and the like has not been studied at all, and there is no report on the improvement of dispersibility to enhance the effect thereof by combining the compound with α-cyclodextrin.
JP-A-5-186419 discloses N,N′-bis(hexadecanoyl)-L-cystine di-tert-butyl ester (compound wherein the group corresponding to R3 and R4 in the formula (I) is a C15 alkyl group) as a synthetic intermediate for a compound usable for vaccine adjuvant; however, its immunomodulatory effect is not reported at all, and there is no report suggesting use thereof as an immunostimulating agent or adjuvant. While both N,N′-bis(hexadecanoyl)-L-cystine dimethyl ester (compound wherein the group corresponding to R3 and R4 in the formula (I) is a C15 alkyl group, CAS registry number: 73793-92-7, described in Cybulla, J. et al., Biochemical and Biophysical Research Communications 1980, 92(4), 1389-96) and N,N′-bis(octadecanoyl)-L-cystine dimethyl ester (compound wherein the group corresponding to R3 and R4 in the formula (I) is a C17 alkyl group, CAS registry numbers: 121074-91-7 and 896442-54-9, described in Zeelen, F. J. et al., Recueil des Travaux Chemiques des Pays-Bas et de la Belgique 1958, 77(3), 267-72) are known compounds; however, their immunomodulatory effects are not reported at all, and there is no report suggesting use thereof as an immunostimulating agent or adjuvant.
On the other hand, Y. Aachoui et al., Cellular Immunology 271 (2011) 308-318 reports the results evaluating the adjuvant activity of phytol and a derivative thereof. This document describes that β-cyclodextrin was used for dissolving phytol in cell proliferation inhibitory assay; however, β-cyclodextrin was not used for the evaluation of antigen-specific antibody production. In addition, α-cyclodextrin is not described or suggested in Y. Aachoui et al., Cellular Immunology 271 (2011) 308-318.
Thus, there remains a need for compounds which have a superior immunostimulatory effect and are useful as an immunostimulating agent, particularly an adjuvant. There also remains a need for compositions containing such a compound, and vaccines containing such a compound and an antigen.